The present invention relates to a trouble diagnosis system for a motor vehicle.
Recently, a motor vehicle has been equipped with an electronic control system for controlling various components of an engine, such as fuel injectors, thereby improving driveability, exhaust gas emission, fuel consumption, and engine power. The electronic control system controls the components based on information represented by output signals from various sensors for detecting engine operating conditions. Accordingly, if malfunctions of components and sensors occur, the engine does not properly operate.
Japanese Patent Application Laid Open 59-61740 discloses a self-diagnosis system where signaling lamps provided on the vehicle are lit or flashed when abnormalities occur in sensors and actuators such as injectors. However, the nature of the defective condition of the sensors and actuators cannot be known only by the lit or flashing lamps. Accordingly, a trouble diagnosis device for easily checking the electronic control system should be provided as equipment in an auto shop.
Japanese Patent Application Laid-Open 58-12848 discloses a diagnosis system in which a checking device is provided for measuring the pulse duration of fuel injection and an engine speed, and for checking whether idling speed is normal.
However, the system is provided for diagnosing only a designated type of motor vehicle by using an exclusive checking device.
In order to diagnose various vehicles, it is necessary to provide several types of checking devices corresponding to respective types of motor vehicles.
FIG. 6 shows a recently proposed diagnosis system which comprises a diagnosis device 102 and a memory cartridge 103 detachably attached to the device 102. The memory cartridge 103 has a memory such as a ROM for storing diagnosis programs and fixed data for the type and the model year of a vehicle 100. Various cartridges 103 (only one being illustrated) for all vehicle types are provided and the cartridge for the presented vehicle is selected and attached to the diagnosis device 102. A two-way communication between the cartridge 103 and an electronic control system 101 on the vehicle 100 is performed for diagnosing the electronic control system.
However, since the program stored in the fixed capacity ROM of the cartridge in the system can not be expanded for additional functions, if additional sensors and actuators are mounted on the motor vehicle, the control system can not diagnose the additional equipment. Further, in the case where a plurality of input signals from the control system must be simultaneously calculated and treated by the diagnosis device, such operations can not be performed by a single device, even if the memory cartridge is changed. Further, there is a weakness in that if the two-way communication system between the control system and the diagnosis device is changed, the diagnosis device can not diagnose it.